A variety of supplemental recovery techniques have been employed in order to increase the recovery of viscous oil from subterranean viscous oil containing formations. These techniques include thermal recovery methods, waterflooding and miscible flooding, particularly CO.sub.2 flooding.
In heterogeneous hydrocarbon containing subterranean formations, i.e., formations having relatively high permeability zones and relatively lesser permeability zones, tertiary oil recovery processes are relatively inefficient because fluids preferentially migrate into the highly permeable zones in the subterranean formations. Migration described above is undesirable when injecting treatment fluids into oil-containing formations for the recovery of oil since the treatment fluids channel through the highly permeable zones, bypassing the less permeable zones. The result is poor conformance and flow profiles of the treatment fluid in the formation. The hydrocarbons residing in the less permeable zones are not produced and the overall yield of hydrocarbons from the formation is reduced.
To increase the efficiency of formation flooding processes, the highly permeable zones in a subterranean formations are plugged or partially plugged to prevent or reduce migration of treatment fluids into them and to divert treatment fluids into adjacent, less permeable zones. In injection profile control projects, polymeric materials have been used in liquid slurries or suspensions to effectively enter and plug or partially plug the highly permeable and/or fractured zones of the formation. Fluids injected after such a treatment therefore move into upswept areas or zones of the reservoir which results in increased oil recovery.
In my U.S. Pat. No. 4,458,760 there is disclosed a process for improving oil recovery from stratified reservoirs by (1) injecting low salinity water to reduce the salinity in high permeability zones, (2) injecting a surfactant solution into the high permeability zones, (3) injecting high salinity water into the reservoir, thereby forming a surfactant/water/oil emulsion which reduces effective brine permeability in the high permeability zones, and (4) continuing to inject high salinity water into the reservoir, whereby water is diverted to low permeability zones and oil is recovered from the low permeability zones. Low salinity water may then be injected to break-up or release the emulsion in the high permeability zones and to recover oil from the high permeability zones.
In the process of my present invention, a surfactant is injected into the formation that preferentially enters the highly permeable zones and produces a gel in-situ in the formation via interaction of the injected surfactant and subsequently injected CO.sub.2 under the temperature, salinity, oil composition and CO.sub.2 pressure conditions within the formation. Formation of the gel substantially plugs or partially plugs the highly porous zones to reduce channeling of injected CO.sub.2 through these zones, and to divert CO.sub.2 to lower permeability zones which would otherwise be by-passed by the CO.sub.2 thereby resulting in more complete displacement of oil from the formation.